Soffit vents help assure attic ventilation, reducing moisture and heat problems—but they tend to worsen the destructive action of hurricane-force winds. Rain can be wind-borne through the vents into the attic or such roof space, causing ruinous mould and even ceiling collapse, and in common house configurations the soffit vents can allow roof space pressurization that increases the net outward pressure that can blow apart the roof envelope.
If soffit vents are valved, however, their role in hurricane winds can be changed from harmful to helpful. In U.S. Pat. No. 6,484,459 B1, “Counter-Pressure Method and Apparatus for Protecting Roofs against Hurricanes”, Platts discloses how valving soffit vents can not only prevent roof space pressurization in strong winds but can ensure wind-induced depressurization therein, which “counter-pressures” the wind's “suction” above and around the roof, thereby reducing the net outward pressures on the roof envelope and so helping keep it all intact—roof sheathing down, gables on, soffit and ceiling up. The depressurizing action is simple and strong (given that gross air leaks are sealed and other roof vents are closed off or are themselves valved); while the valves in windward soffit vents blow closed in strong winds, the soffit vents around the wind-depressurized lee sides of the house remain open, leaving the roof space connected only to the lee side air and so itself depressurized.
In the referenced patent, Platts scarcely touches upon the valve design issue. A “hanging flap” valve for soffit vents is sketched therein, simply to help illustrate the depressurization idea; such a normally-open valve hanging below a soffit would be prone to “missile” damage in hurricanes and would be objectionably noisy in gusty winds. The noise problem dogged all designs, starting with an above-soffit single-flap valve developed for the first lab and field trials of Platts' counter-pressure idea. Foam rubber dampers failed to muffle the hinged flap's “whumph” noise in gusty winds. (The householders therefore chose to lock the valves open, thus requiring their presence at home to unlock them if a storm threatened—losing their “always ready” advantage.)
Accordingly, to reduce the flap mass and hence the noise problem, and also to reduce height so the valved vents could fit into shallow soffit spaces, common multi-flap “vent cap” valve products were adapted for further valved-vent lab and field trials. The small flaps must still be fairly substantial, however, since they span beam-like across the opening, pin-hinge-supported only at their ends. Further, they're still hinged flaps, with their free sides swinging fast and closing against small areas, so they still operate noisily. And airflow under and through such louver-type flaps tends to set up “flutter”: their sounds simply become a higher-pitched “flap” or “rat-a-tat” clatter, again calling for fussy insertion of resilient felt or foam dampers—which still prove rather ineffective.
More problems: Most ways of valving a vent tend to restrict flow, the open area becoming considerably less than the vent's overall plan area. So a required venting area must use bigger vents or more of them, adding more cost of parts and installation. (Primary example: building codes commonly require a total “net free area” for roof space ventilation. While common insect screens block 50% of an opening's area, 70%-open screens have been developed for roof space vent grilles to help provide such net free area more economically.) Valve responsiveness is of concern too: reliable and speedy closure are important but not readily assured with multi-flap designs.
Looking further into the prior art of fluid flow control valves, the main examples are as old as plant and animal life, where nature offers the original and marvelous flap, gill, tongue, throat, diaphragm and even ball valves. Man adapted these and added more, including butterfly, reed, rotary, slide or sleeve, needle and poppet-orifice valves, meeting a very wide range of flow-control needs.
Gally, in U.S. Pat. No. 1,271,562, AIR PUMPER CHECK, Jul. 9, 1918, invented a quiet, relatively free-flow “V” 2-flap check valve (for Baldwin player pianos) that's not, however, readily adaptable to a normally-open stance offering two-way unimpeded flow.
In U.S. Pat. No. 3,895,646, Jul. 22 1975, SELF REGULATING VANE TYPE VALVE FOR CONTROLLING AIR FLOW, Howat describes a quiet-acting building ventilation control valve offering flow modulation passively adjusted by temperature and/or air pressure differentials, say, using bi-metallic or simply springy “V” shaped vanes arranged in a cone fashion. It's not intrinsically good for two-way ventilation, being relatively flow-restrictive even if made to stand somewhat open for normal two-way ventilation.
Foley, in U.S. Pat. No. 5,842,503, Dec. 1, 1998, INTEGRALLY FORMED AIR FLOW VALVE, describes a light, quiet and inexpensive valve expressly for one-way relief of door-slamming pressure effects in automobiles. It offers a series of V valves that could well fit the spatial and structural requirements of soffit vents for roof spaces, with the V's somewhat modifiable to allow two-way flow, but again with excessive impedance to venting flows so that the valve would have to be very large to provide a given flow path.
Another simple, quiet valve is presented by Bowers et al., in U.S. Pat. No. 7,448,219 B2 Nov. 11, 2008, HINGELESS FLAPPER VALVE FOR FLOW CONTROL. The self-hinging, self-actuating valve (very much like a tongue housed in a mouth-and-throat vent passage) can be normally open to two-way flow, but again is much too flow-restrictive for present purposes even if considerably modified, say by extensive widening.
There are also inexpensive multi-layer diaphragm valves offering two-way flow under light pressure differentials while finally closing tightly against high-pressure one-way flow. In U.S. Pat. No. 7,694,701, STRUCTURE OF CHECK VALVE FOR AIR-PACKING DEVICE, Apr. 13, 2010, Koyanagi describes a unique assembly that becomes a part of plastic pressure packs—but once again the flow paths are inherently restrictive.